The most popular type of scale sold has for many years been the flat, compact and portable bath scale which is both inexpensive and reasonably accurate for measuring variations in ones body weight. The scale typically includes a flat, rectangular base pan over which a load receiving platform is supported. The lower pan includes peripherally disposed upstanding walls while the platform has peripherally disposed downwardly extending walls which surround the walls on the pan to form an enclosure within which the force collecting and indicating mechanism is disposed.
In the typical scale, there are four force collecting levers which are pivoted in the corners of the base pan and which are interconnected to deliver the sum of the forces on the platform to a pate which bears downwardly on a helical load spring supported by the pan. The amount of deflection by the load applying plate is recorded by a mechanism which generally rotates a dial calibrated to indicate the weight applied to the platform.
Such scales must normally include a zero adjustment mechanism associated with the indicator so that the user may adjust the indicator dial to zero before stepping onto the scale. The scales also normally include a factory calibration adjustment which allows the scale to be calibrated to take into account the variations in the load spring which may be used in the scale.
Since there are many more sophisticated bath scales available which utilize strain gauges and digital output to provide more accurate weight indications, the manufacturers of mechanical bath scale have been under severe pressures to reduce prices in a very competitive product area. Accordingly, manufacturers have consistently attempted to simplify the force gathering means, the indicating mechanism and the calibration and zeroing mechanism. There has also been a trend in the industry toward providing thinner and more compact scales, thereby requiring that the internal mechanisms be made more compact.
One example of an early, thin and structurally simple scale is shown in the recently issued Baccini U.S. Pat. No. 4,643,266. Other prior art patents showing the general type of force collecting means, calibration means and zeroing means with which the present invention is concerned are the U.S. Pat. No. 3,759,338 to Petersen et al., and U.S. Pat. No. 3,426,861 to Provi.